Seismic exploration methods that are used today require the recording and evaluation of a large amount of field data, which as a rule are received by geophones or hydrophones. A typical recording system uses 256 traces which are allocated to individual geophones, hydrophones or groups of receivers.
As a rule the signals that are received are recorded in a time division multiplex process on a storage medium, the recording on the magnetic tape itself taking place in the form of nine parallel tracks.
A body of data recorded in accordance with the process cited is, as a rule, subjected to various corrective measures, such as dynamic and static corrections, stacking or something similar, before its final presentation. This does not take place in the field but only in the computer center.
For evaluation and analysis of the seismic traces, the traces allocated to individual receivers or receiver groups (e.g. 256) are recorded side by side, commonly on a paper carrier, the amplitude of a trace being represented perpendicular to the time axis. For better legibility the areas under the positive half-waves of the trace are often blackened, i.e. a so-called thickened notation is formed. Representations of the seismogram on screens are also possible.
Thickened notation representations of this kind can be found in the company publication of applicant's assignee, Prakla-Seismos AG, Information No. 10, dated 1978. Along with a blackening of half-waves a colored accentuation, also in thickened notation, is also provided for identifying distinguishing special amplitude values. This representation was chosen in order to improve the amplitude resolution in such seismograms, which are inherently inadequate for certain actual amplitudes.
This publication deals exclusively with possibilities of being able to undertake the most varied evaluations of the data that have been recorded in a computer center. In this process, however, neither an immediate qualitative nor a quantitative rough estimate of a measured pattern is possible during the field operations. If it should turn out during subsequent evaluation in the computer center that certain receivers or groups of receivers malfunctioned during the recording, repetition of the recording is only possible with substantial effort and cost.
Although the process described makes possible precise and effective evaluation of seismic signals, the fact that the evaluation is only undertaken after the fact is rather an obstacle for field operations, in particular with regard to monitoring the reliability of the individual measurements. If one wishes to determine during a seismic measurement or immediately afterward whether the measurements being undertaken are within a prescribed tolerance range, whether the signals of individual receivers or groups of receivers are outside the expected signal ranges or whether there are defective receivers or receiver installations, this process cannot be used.
Although a device for testing outlying geophones that are attached to a seismic receiving device is known from German Patent No. 26 44 886, the detection of errors that have occurred does not take place directly on the basis of field signals that are received but through the aid of artificial signals. Hence, substantial additional expenditure is required for this kind of testing of the operability of geophones.
U.S. Pat. No. 3,458,859 cites a process for comparing the traces of seismograms that were obtained from a digital data transmission format with amplification control. In the process the original amplification factor, which was in steps, is replaced by an interpolation function for output. This device has nothing in common with the invention.
German prosecuted patent application No. 20 40 296 shows a process for representing geophysical values on a two-dimensional surface, the recording being in the form of a color representation. In that process there is no usable representation on a cathode ray tube, but the latter serves only as a transmission means in which the information portrayed on the screen of a cathode ray tube is transmitted via a cylinder lens to a drum recording device.